转向注水改善特低渗油藏开发效果

Converting Direction of Water Flooding to Improve Development Response of Ultra-low Permeability Oil Reservoir

针对卫城油田沙四段油藏进入高含水开发后期,受裂缝发育影响,平面、层间矛盾日益突出,含水上升速度加快、开发形势变差的状况,开展油藏精细描述研究工作,重点研究地应力-裂缝对开发的影响,认识到注采井网不适应是该油藏高含水开发后期的主要问题。在剩余油研究基础上,一是通过实施避开裂缝方向优选转注井点,转换注采方向,使注采方向与裂缝方向成45°夹角注水;二是通过打塞、挤堵、重分、差层转注等手段,抽稀Ⅰ类层井网、建立差层井网,同时改变Ⅰ类层和Ⅱ、Ⅲ类层的注水强度,实现了卫城沙四段特低渗油藏高含水开发后期"转换注水方向、转换注采井别、改变注水强度"的转向注水。通过研究及应用,使卫城沙四段特低渗油藏注采井网逐步优化,水驱控制程度、水驱动用程度分别提高7.5和5.4个百分点,油藏综合含水下降0.4%,日产油量由135t/d回升到154t/d,自然递减率同期对比减缓7.62个百分点,增加可采储量10.5×104t,提高采收率1.45个百分点。

In the later stage of high water cut,the contradiction of planes and interlaminations has become an increasingly prominent issue and the rate of water cut has risen faster and the condition of development has become worse effected by growing fractures in the reservoir of member 4 of Shahejie formation in Weicheng oilfield.According to the above,fine reservoir description is studied mainly focusing on the effects of crustal stress- es and fractures on oilfield development.We come to realize that the inadaptation of flooding well network is the main problem during the later developing period of high water cut in oil fields.Based on remaining oil study,firstly,injection wells are optimized and direction of injection-production is changed through avoiding crack direction,which makes 45~angle between direction of injection-production and crack direction.Secondly, well pattern of class I layers is thinned and well pattern of poor layers is established by means of block- ing,squeezing and plugging,rezoning and converting injection in poor layers,and injection strength will be changed in class I layers and class 11 and 111 layers.Finally it is realized that the converting direction of wa- ter injection,converting wells of injection and production and adjusting strength of water injection in the ul- tra-low permeability oil reservoirs of the fourth member of Shahejie formation of Weicheng in the later period of high water cut production.Through research and application, injection-production well pattern has been grad- ually optimized ,the control level of water drive and the production level of water drive have been improved by 7.5% and 5.4% respectively in the ultra-low permeability oil reservoir of the fourth member of Shahejie formation ,Weicheng.The composite water cut of the oil reservoir has been declined by 0.4% ,and daily oil pro- duction rose from 135t/d to 154t/d.Natural decline rate compared with that in the same period has been slowed down by 7.62% and increased recoverable reserves is 10.5×10^4t,and oil recovery efficiency enhanced by 1.45%.